Voltage tunable magnetron



March 29, 1960 a. J. GRIFFIN, JR,, EI'AL 2,930,933

VOLTAGE TUNABLE MAGNETRON 3 Filed March 25. 1958 INVENTORS 2 GERALD J.GRIFFIN,JR.

DAVID J. HODGES, CARMINE MIGLORE ROBERT P WATSON THEIR ATTORNEY.

United States Patent VOLTAGE TUNABLE MAGNETRON Gerald J. Gritfin, Jr.,and Robert P. Watson, Schenectady,

Carmine Miglore, Scotia, and David J. Hodges, Saratoga, N.Y., assignorsto General Electric Company, a corporation of New York 3 ApplicationMarch 25, 1958, Serial No. 723,926

11 Claims. (Cl. SIS-39.63)

The present invention relates to an improved magnetron device tunable byvariation of the anode-cathode voltage and more particularly to suchdevices including improved means for controlling the tuning andincreasing the operating efiiciency thereof and for better adapting suchdevices for operating under extreme vibratory and low-pressureatmospheric conditions.

In US. Patent No. 2,810,096, entitled Voltage Tunable Magnetron WithControl Electrode, to P. H. Peters, In, et al., and assigned to the sameassignee as the present application, is described and claimed a voltagetunable magnetron having a control electrode for determining the powerlevel at which the voltage tunable operation takes place. In accordancewith that invention, the magnetron is provided with an emitting cathodearea physically located outside of the oscillatory circuit, of which theanode is a part, and surrounded by a control electrode for determiningthe space charge within the anode and as a result of the output powerlevel. The end of the control electrode is physically very close to theanode, in an axial direction, and is shaped to provide an axialcomponent of field to assist in injecting the electrons from the regionsurrounding an emissive portion of the cathode and into m interactionspace between the anode and the non-emissive portion of the cathodewhile at the same time keeping the electrons collected by the controlelement to a minimum. In the interaction space the movement of theelectrons and the energy transferred therefrom is determined by thestrength of the axial static magnetic field. I

The present invention is in the nature of an improvement over theinvention described and claimed in the aforementioned patent and relatesto the provision of means adapted for insuring against adverse effectsof filament current on the control of the device as effected by thementioned control electrode and on the operation of the device asdetermined by the axial static magnetic field. Additionally, in thepresently contemplated device the emissive and non-emissive portions ofthe oathode can be physically and electrically spaced enabling operationthereof at different potentials. Further, in the present device meanscan be included for rigidizing the mounting of the emissive cathode.Still further, the same rigidizing means can be employed, where desired,for electrically connecting the emissive and non-emissive cathodes andthus assisting in predetermining the field configuration in the regionthrough which the electrons must pass by injection into the interactionspace, thereby to facilitate such injection and minimize undesirablecollection of electrons on the end of the non-emissive cathode. Thepresent device is also better adapted through electrode dimensioning anddisposition relative to insulative members for increasing and makingindirect the creepage path between electrodes of different potentials,thereby better to adapt the device for high altitude operation.

Accordingly, an important object of our invention is to provide a newand improved voltage tunable magnetron ice including new and improvedmeans for controlling the injection of electrons into the interactionspace of the therein are self-annulling or cancelling, thus to minimizeadverse effects on the operation of the tuning means thus on the radiofrequency of the device.

Another object of the present invention is to provide, in a voltagetunable magnetron including a filamentary cathode, new and improvedmeans for rigidizing the cathode and adapted for assisting inpredetermining the field configuration in the region surrounding thecathode.

Still another object of the present invention is to provide a new andimproved stacked arrangement of electrodes and insulator elementswhereby production may be facilitated. and the device is better adaptedfor high altitude operation.

Further objects and advantages of our invention will and become apparentas the following description proceeds and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

For a better understanding of our invention reference may be had to theaccompanying drawing in which;

Figure l is an enlarged elevational view in section of a magnetrondevice embodying our invention;

Figure 2 is a fragmentary sectional view of a modified form of ourinvention;

Figure 3 is a fragmentary sectional view of another modified form of ourinvention; and v Figure 4 is a fragmentary sectional view of stillanother modified form of our invention.

Referring now to the drawing, there is shown in Figure 1 amagnetrondevice embodying a form of our invent-ion. The device of Figure 1includes an envelope generally designated 1 and constituted of a stackedassembly of alternately arranged metal and ceramic members wherein someof the metal members serve as electrioal terminals of the device and theceramic members serve as insulative spacers between the metal members.

The metal members 'which serve as electrical terminals include a pair ofannular anode terminals 2 and 3, sepa rated bya ceramic cylinder 4. Themetal members further include a frusto-conical control electrode 5 whichwill "be described in greater detail hereinafter and which includes aflanged or annular portion 6 separated from anode terminal 3 :by meansof a ceramic cylinder 7 which is of a substantially greater outerdiameter than the flange 6. The smaller diameter of the flange 6relative end member 10 separated from the anode terminal} by a ceramiccylinder 11. The end member 10 com prises a centrally bored metal cap 12in which is suitably fitted and bonded an internally extending post 13.The post 13 comprises the cold or non-emitting cathode assembly of thedevice which :will be described in greater detail hereinafter, and themetal cap 12 comprises an electrical terminal therefor, Additionally, asillustrated,

3 the outer diameter of the cap 12 is substantially less than that ofthe ceramic insulator 11. This arrangement increases the leakage pathbetween the cold cathode terminal and the anode terminal 2, and, thus,also adapts the device for high altitude operation. The other end of theenvelope 1 is completed by a ceramic or disk 14. The disk 14 supportsthe hot cathode or electron emitter 15 of the device which will bedescribed in greater detail hereinafter.

The magnetron device illustrated is of the interdigital type in whichthe anode assembly includes two sets of axially extending anode segmentsalternately arranged in a cylindrical array supported concentricallywithin the envelope 1 by the anode terminals 2 and 3. Alternate segments16 and 17 are connected to different ones of the annular anodes 2 and 3,respectively, thus to provide two groups of anode segments alternatelyarranged in the array with each group connected to one of the terminals2 or 3. The segments are slightly separated to provide axially extendinginteraction gaps. As is well understood in the art, it is theinteraction between the high frequency fields across these gaps and therotating and bunched space charge that effects the desired energytransfer from the space charge to the oscillatory circuit of the anode.As is also well understood in the art the electron rotation results fromthe provision of an axial magnetic field through the device. Such afield is usually provided by disposing the magnetron between the opposedpoles P of a magnet in the manner illustrated in Figure 1.

In the embodiment illustrated, the electrons constituting the rotatingbeam are emitted from a portion of the cathode assembly disposed in aregion of the envelope longitudinally displaced from the array of anodesegments, and the entrance of the electrons into the region of theinteraction gaps is under control of the control electrode 5.

As illustrated in the drawing, the cathode assembly includes thenon-emitting cylindrical post 13 supported from the metal cap orterminal 12 and extending concentrically within the array of anodesegments. As shown, the post 13, which may be referred to as the coldcathode, inasmuch as it does not emit electrons, is fitted in a centralbore 20 in a concentric internally extending boss 21 formed on the cap28. In this arrangement the cap 12 and the post 13 may be formed oftitanium and the assembler of the device may easily adjust the desiredextension or protrusion of the post into the envelope, lock the post inthe desired adjusted position by spot welding and subsequently fullybonding the post in the end cap by brazing in a vacuum with the use of anickel or copper ring between the post and end cap. As also shown, theboss 21 extends to the immediate vicinity of the array of anode segmentsand thus serves as an end shield for the interaction space. The post 21extends longitudinally into the interaction space and terminates thereinslightly inwardly of the lower end of the anode array, as viewed inFig. 1. The axial spacing of the lower ends of the cold cathode andanode array is preferably about mils.

Coaxially arranged in the lower end of the envelope 1 and longitudinallydisplaced from the lower end of the post or cold cathode 13 is theaforementioned hot cathode or emitter 15. The hot cathode is of thedirectly-heated filamentary type and preferably is formed of thoriatedtungsten wire and spaced about 10 mils from the cold cathode. Thecathode 15 is bifilar and contrawound or, in other words, comprises adouble helix structure wherein the helices are mutually oppositelywound. In this structure both ends or leads 22 of the filament aredisposed at one end thereof and the hot cathode is mounted and solelysupported in the envelope by means of the leads 22. The leads 22 includeportions which extend radially substantially from the axis of thecathode, thereby to increase stability and resist- 4 ance to vibratorymovement, and downward extending portions which extend through and aresuitably sealed in apertures 23 parallelly extending in spaced relationthrough the ceramic disk 14.

Connected to the outer extremities of the leads 22 is a pair of contactbuttons 24. The buttons 24 are preferably formed of titanium and havethe ends of the leads suitably brazed therein. Additionally, the buttons24 are brazed to the outer surface of the ceramic disk 14 as bydisposing a nickel shim between each of the buttons 24 and disk 14 andraising to a brazing temperature in a vacuum. The buttons 24 areeffective for completing an electrical circuit through the contra-woundfilamentary cathode, thereby to render same emissive and provide a cloudof electrons about the filament in the lower region of the device.

The just-described hot cathode arrangement including the bifilarcontra-wound helices enables the hot cathode to be energized practicallyfrom either a D.C. or A.C. source. Thus, the device is not limited tothe use of a D.C. source in operating the filament as is the case wherea single helix or multiple helices wound in the same direction areprovided. If an AC. source were utilized with the latter type offilament, the fields set up by the filamentary current may deleteriouslyaffect the RF. operationof the device. In the contra-wound filament ofthe present device, the fields set up by the filament current areself-annulling or effectively cancel each other and, thus, are less aptto affect undesirably the radio frequency operation of the device. Theparticular manner in which this greatly enhances the operation of thepresently disclosed device will be brought out in detail hereinafter.

As illustrated, the buttons 24 are disposed substantially inwardly ofthe edges of the ceramic disk 14, which arrangement serves to increasethe leakage path to the anode contacts and adapts the device for highaltitude operation. In the operation of the disclosed device, theelectrons constituting the cloud surrounding the filamentary cathode arecaused to enter or be injected into the interaction space between thenon-emitting or cold cathode 13 and the cylindrical array of anodesegments 16 and 17. This injection of electrons is under control of thecontrol electrode 5 which will also be described in greater detailhereinafter.

Also brazed to the lower sides of the ceramic disk 14 is a controlelectrode contact button 26. The button 26 is brazed to the disk 14 inthe same manner as the buttons 24. Additionally, the button 26 issuitably electrically connected to a tantalum or tungsten lead 27 whichextends through and is sealed in a suitable aperture 28 extendingthrough the disk 14 in parallel spaced relation to the aperture 23. Theupper end of the aperture 28 opens directly beneath the flange 6 of thecontrol electrode 5 and the upper or inner end of the lead 27 issuitably electrically connected to the flange 6, whereby the button 26is adapted for serving as the contact for making an electricalconnection to the control electrode 5. Additionally, the provision ofthe lead 27 extending through the ceramic disk 14 and the controlelectrode contact button 26 better adapts the device for high altitudeoperation by making it possible to avoid reliance on the flange 6 formaking electrical contact to the control electrode, and, thus, enablingthe outer diameter of the flange 6 to be reduced and disposedre-entrantly between the ceramic insulators 7 and 14. It will be seenfrom the foregoing and as illustrated in Fig. 2 that, if desired, theflange 6 can be completely irnbedded in the envelope wall by beingpositioned in a counterbore or recessed edge 7a provided in the lowerend of the ceramic insulator 7 and an annular recess 14a provided in theupper surface of the ceramic disk 14. Thus, the only possible externalleakage path between the anode and the control electrode 5 would be thesubstantially elongated path extending between the anode contact 3 andthe control contact button 26 over the outer surfaces of the ceramics 7and 14.

The control electrode 5 includes, in addition to the flange 6, a tubularportion 30 extending from the flange 6 thereof toward the interactionspace of the device. The tubular portion 30 is frusto-conical in shapeand includes an inner surface which is spaced progressively closer tothe filamentary cathode 15 in an axial directiontoward the anodeassembly. In operation, the control electrode 5 is maintained at apositive potential with respect to the cathode so that an axialcomponent of velocity toward the interaction space is imparted to theelectrons emanating from the hot cathode 15. As illustrated, thefrustoconical portion of the control electrode terminates in closelyspaced relation to the anode. This spacing is preferably about 10 mils.Additionally, and as also illustrated, the control electrode is providedwith a short internal cylindrical surface 31 adjacent the anode. Thecylindrical surface 31 is preferably about 20 mils in length and has adiameter at least equal to and preferably smaller than that of thecylinder defined by the inner surfaces of the anode segments. Thisarrangement minimizes back-heating of the cathode and undesirableelectron impingement and collection on the lower ends of the anode arrayand cold cathode.

The particular configuration of the control electrode and the particularspacing of the various portions thereof from the anode contributesubstantially to its effectiveness in injecting a substantial number ofelectrons into the interaction space between the cold cathode 13 and theanode segment. This is particularly desirable in voltage-tunablemagnetron devices since under the conditions existing during suchoperation the high frequency fields between adjacent anode segments arerelatively weak in comparison with those existing in tank-tunedoperation. In the specific embodiment of the device illustrated in Fig.l, the wall of the control electrode extends at an angle ofapproximately 30 degrees with respect to the axis of the conical portionand the cylindrical portion 31 of the control electrode has an axiallength of approximately 20 mils. The spacing between the face of theanode and the inner end of the control electrode is approximately 10mils, and the inner end of the hot cathode extends beyond the controlelectrode and is spaced from the cold cathode approximately 10 mils.

In operation of the above-described device, a static magnetic field isprovided by the magnetic poles P which field extends axially through thedevice. This magnetic field may be in the order of approximately 2500gauss and is effective for rotating the electrons which are injectedinto the interaction space, thereby to effect the above-described energytransfer to the anode segments. The anode voltage at center frequencymay be approximately 1150' volts, the filament current may be D.C. andapproximately 3 amperes, and the control electrode potential may be +300to +500 volts. Under these conditions of operation, the controlelectrode will be effective for injecting the electrons into theinteraction space and the frequency of the device may be tuned byvarying the potential between the anode and cathode.

It has been found that in voltage-tunable magnetron devices utilizing asingle helix emitter or a multi-helix heater wherein the helices arewound in the same direction, magnetic fields are set up by the filamentcurrent which affect the main axial static magnetic field and thus causeundesirable proportional changes in the operating 6 change the radiofrequency amplitude of the operating frequency and the operatingfrequency of the device.

In our device and as described above, the hot cathode comprises abifilar contra-wound element or in other words, a double-helix filamentwherein the helices are mutually oppositely wound. Thus, the magneticfield' set up by the supply current thereof is self-annulling or, in

other words, the contra-wound filament effectively cancels bothcomponents of the field established therebetween, and, therefore cannothave any of'the above-described deleterious effects on the main axialstatic magnetic field or on the operation of the control electrode ininjecting electrons into the interaction space. Thus, the device isadapted for improved operating efficiency.

In some applications the disclosed device is subject to considerablevibration. Under such conditions it is desirable to provide means forminimizing vibration of the filamentary cathode relative to the otherelectrodes. It is particularly desirable to minimize relative movementbetween the filamentary cathode and control electrodes since suchmovement would tend to result in non-uniform injection of electrons intothe interaction space about the cold cathode and thus affect undesirablythe tuned operating frequency of the device. In the sense that the tunedoperating frequency of the device can be adversely affected by changesin the spacing between the cathode and control electrode, the operationof the device is most sensitive to motion of the cathode in theinjection region. Additional-1y, excessive motion of the filamentarycathode can cause fatigue and resultant fracture thereof. Motion of thefilamentary cathode is minimized and the cathode is made more stable bythe disposition of the leads 22 substantially outwardly of the axis ofthe cathode in the manner shown in the drawing.

Illustrated in Fig. 3 is a modified form of our invention adapted forrendering more rigid the mounting of the filamentary cathode and thusminimizing any tendency toward vibration thereof and its undesirableeffects. In this embodiment the same numerals designate the same orsimilar elements as those shown in Fig. 1 and described above.

However, as seen in Fig. 3, the relative longitudinal positions andspacing of the various electrode elements can be different. In thedevice of Fig. 3, control electrode 5 is spaced about ten mils from theanode, the upper end of the hot cathode 15 is about coplanar with thelower edge 32 of the 20 mils long cylindrical surface 31 of the controlelectrode, and the cold cathode 13 extends slightly into the controlelectrode and is spaced about 10 mils from the hot cathode. In thisarrangement, substantially all electrons emanating from the hot cathode15 are under the control of the electrode 5 in the injection of suchelectrodes into the interaction space.

The means provided for rigidizing the mounting of the filament 15 in thedevice of Fig. 3 comprise a support rod 33. The support rod 33 iscentrally disposed in the contra-wound filament 15 and, as shown, islongitudinally talum tube 34 which, in turn, is fitted and brazed in acentral aperture 35 extending through the filament disc 14. The outerend of the tantalum tube 34 registers substantially with the under sideof the ceramic 14, and brazed to the outer end of the tube 34 as well asto the under side of the ceramic 14 is a titanium cap 37. This structureinsures a vacuum-tight seal about the support rod and tube. tage to betaken of the low heat conductivity of tantalum for eliminating hot spotsin the filament ceramic which could cause cracking and leaking.

The inner end of the support rod 33 has the contra- V wound filamentsecured thereto as bydisposition of the 1 f Additionally, it enablesadvan-' cross-over portion of the filament in an end slot 38 in the rodand either welding of the cross-over portion in the slot or crimping ofthe end of the post over the crossover portion.

In the structure of Fig. 3, the support rod 33 rigidizes the mounting offilament 15, and, thus, tends to insure substantially uniform spacingbetween the filament and the control element and to maintain thefilament and the cold cathode coaxially under conditions of vibration ofthe device. Thus, the device is adapted for insuring that the amount ofelectrons injected into the interaction spaced between the cold cathodesand anode assembly is substantially uniform about the circumference ofthe cold cathode whereby undesirable changes of the tuned frequency dueto non-uniformity of the electron cloud entering the interaction spaceare minimized. Additionally, the mechanical and electrical isolation ordisconnection of the filament and cold cathode avoid any possibility ofnoise problem due to uncertain electrical contact between the coldcathode and support rod which could occur where these elements areadapted for being in contact.

In some forms of the present device, however, it is desirable andadvantageous from the mechanical and electrical standpoints to connectthe filament support rod and cold cathode. Such a device is illustratedin Fig. 4 wherein, except for the just-mentioned difference, thestructure is substantially similar and the same numerals designate thesame or similar elements as those shown in Figs. 1 and 3. In thisembodiment, the spacing of electrodes is the same as shown in Fig. 3.Additionally a molybdenum support rod 40 is provided. The support rod 40is centrally disposed in the contra-wound filament and the lower endthereof is fitted and brazed in a central recess 41 formed in the uppersurface of the filament ceramic 14. The inner end of the rod 40 isprovided with an end slot 42 in which is disposed the cross-over portionof the contra-wound filament. The cross-over portion of the filament issecured to the rod by either crimping the slotted end of the rod orwelding the filament to the rod in the slot. In the final assembly theupper end of the post is fitted snugly in a central recess 43 in thelower end of the cold cathode. This type of fitting assures asatisfactory rigid electrical contact between the cold cathode andfilament support rod and the arrangement is thus adapted for minimizingnoise problems in the device that could result if a poor mechanicalconnection existed between these elements.

In the device of Fig. 4 the rod 40 enhances greatly the mechanicalrigidity of the filament and also enables all electrical contacts belowground potential to be brought out of the envelope at one end thereof.The greater mechanical rigidity affords greater uniformity in spacingbetween the filament and control electrode during operation, thus toinsure substantially uniform electron injection in the interaction spacethereby to avoid undesirable frequency changes due to variations inelectrode heat injection about the cold cathode.

Additionally, in the structure of Fig. 4 the non-emissive post or coldcathode 13 has a potential midway between the potentials of the filamentterminals. This results in a unipotential conducting surface in both theaxial and radial directions in the region where the electrons areinjected into the interaction space. This type of cathode surfaceassists in providing a more uniform injection of electrons into theinteraction space about the cold cathode thereby to minimize further anytendency toward undesirable changes in the tuned frequency due tonon-uniformity in the amounts of electrons injected.

Still further, the structure of Fig. 4 is effective in reducing theimpingement and collection of electrons on the end of the non-emittingpost or cold cathode. In certain types of operation such a collection ofelectrons on the end of the cold cathode is considered undesirable andsubtracts from the operating efficiency of the device, and contributesto noise. Where such is the case, the structure of Fig. 4 can beutilized to great advantage.

It will be understood from the foregoing that, if desired, thecross-portion connecting the contra-wound helices can be secureddirectly to the end of the cold cathode 13, as by welding in a slotformed in the end of the cold cathode.

In the assembly of the structure shown, active alloy seals arepreferably employed throughout. These seals can be effected by utilizingnickel-sealing shims between the titanium metal elements and between thetitanium and ceramic elements forming a nickel-titanium eutectic sealand titanium sealing shims between the copper and ceramic elements,forming copper-titanium eutectic seals.

In production, the elements are preferably stacked with the appropriatesealing shims interposed therebetween and are brazed and sealed in avacuum furnace at a temperature of approximately 1000 C. Preferably theportion of the device comprising the filaments and filament ceramic areassembled and placed as a separate sub-assembly which includes fittingthe leads of the filament 15 and the control electrode lead 27 into thefilament ceramic l4 and concurrently brazing the leads in the ceramicand brazing the contact buttons to the leads and the ceramic. In theembodiments including the filament support rods, the rods are brazed intheir apertures or recesses during the same sub-assembly brazingoperation.

The next assembly procedure leads to the assembly of the completedevice. This involves placing the end cap 12 in a fixture, then settingthe ceramic cylinder 11 on top of the member 12 with a nickel or coppersealing shim placed therebetween. Then the anode segment 2, ceramicspacer 4, anode segment 3 and ceramic spacer 7 are set in place in thatorder through appropriate guide posts on the fixture withtitanium-sealing shims placed therebetween. Thereafter, the controlelectrode 5 is set in approximate position on and extending into theceramic spacer 7 with a titanium shim therebetween. A stacked unit thusobtained is then inverted on a welding fixture. Then the post or coldcathode 13 is dropped into the aperture 20 in the end cap 12 with anickel or copper shim thereabout, and the post is spot welded lightly ina desired spaced relation with respect to the end of the controlelectrode 5 and as determined by the fixture. The fixture is alsoadapted for centering the control electrode. Then the unit is inverted,the filament sub-assembly is set in place on the flange of the controlelectrode guided by the same posts which align the anode assembly andwith a titanium shim therebetween. Thus, the brazing unit is completedfor transfer into the vacuum furnace wherein the brazing operation iscarried out for effectively brazing the various parts to bond sametogether and thus complete a vacuum-type device.

In assembling the modified structure of Fig. 4 the slotted end of thesupport rod 40 will be snugly fitted into the end of the post 13 whenthe filament subassembly is being placed into position. It will be seenthat this fitting of the support rod in the cold cathode will have adesired effect of holding the brazing unit together until the brazingoperation is complete.

It will be seen from the foregoing that we have provided improvedvoltage tunable magnetron devices adapted for better controlled voltagetuning, increased operation efiiciency, ease in making circuitconnections thereto, higher altitude operation and greater facility inhigh production manufacture.

While we have shown and discussed specific embodiments of our invention,we do not desire our invention to be limited to the particular formsshown and described, and we intend by the appended claims to cover allmodifications within the spirit and scope of our in vention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A magnetron comprising an anode circuit including a plurality ofsegments supported in a cylindrical array in mutually spaced relation, anon-emissive electrode supported concentrically within the openingdefined by said segments, a filamentary electron emissive electrodelongitudinally displaced from said non-emissive electrode andconstituted of a plurality of contra-wound electrically connectedhelices jointly defining a generally cylindrical structure, a controlelectrode surrounding said filamentary electrode, and means disposedbetween said non-emissive and emissive electrodes efiective forminimizing electron impingement and collection upon the end of saidnon-emissive electrode.

2. A magnetron comprising an envelope, an anode circuit including aplurality of segments supported in a cylindrical array in mutuallyspacedrelation, a nonemissive electrode supported in said envelopeconcentrically within and extending into the opening defined by saidsegments, a unipotential bifilar contra-Wound filamentary emitterextending toward and spaced axially from said non-emissive electrode, acontrol electrode surrounding said filamentary emitter, said controlelectrode being closely spaced to said array, and said control electrodehaving an inner cylindrical surface of a smaller diameter than that ofsaid opening defined by said segments, and an additional inner surfaceaxially remote from said array and of larger diameter than saidcylindrical surface.

3. A magnetron comprising an envelope, an anode circuit including aplurality of segments supported in a cylindrical array in mutuallyspaced relation, a nonemissive electrode supported in said envelopeconcentrically within and extending beyond the opening defined by saidsegments, a unipotential bifilar contra-wound filamentary emitterextending toward and spaced axially from said non-emissive electrode, acontrol electrode surrounding said filamentary emitter, said controlelectrode having an inner cylindrical surface of short axial lengthbeing par tially coextensive with said non-emissive electrode andterminating at the outer edge in closely spaced relation to one end ofsaid array and at the inner edge at a point substantially coplanar withthe end of said filamentary emitter, and an additional inner surfaceaxially remote from said array and of larger diameter than saidcylindrical surface.

4. An electric discharge device comprising three insulative cylindersarranged in a stack, three annular metal members, each of a pair of saidmetal members being interposed between adjacent ends of different pairsof said insulative cylinders, a cylindrical array of anode segmentssupported from said pair of metal members within said insulativecylinders with alternate segments connected to one of said pair and theremaining segments connected to the other of said pair, a metallic capat one end of said stack and a ceramic cap at the opposite end of saidstack, the third of said annular metal members being interposed betweensaid opposite end of said stack and said ceramic cap, a unipotential bifilar contra-wound filamentary emitter having all of the ends thereofextending through and sealed in said ceramic cap, and a controlelectrode surrounding said filamentary emitter and supported from saidthird of said annular metal members.

5. An electric discharge device according to claim 4, wherein contactelements are mounted in spaced relation on the outer surface andsubstantially inwardly of the marginal edge of said ceramic cap and havesaid ends of said filamentary emitter connected thereto.

6. An electric discharge device according to claim 4, wherein the thirdof said annular metal members has an outer diameter substantially lessthan the outer diameters of the insulative cylinder and ceramic capbetween which it is interposed, an electrical lead is connected to 10said third member and extends through and is sealed in said ceramic cap,and a contact element is mounted on the outer surface of said ceramiccap and has said electrical lead connected thereto.

7. An electric discharge device according to claim 4, wherein anon-emissive post is supported by said metal cap and extends-toward saidfilamentary emitter in spaced relation to said anode segments, saidcontrol electrode and said metal cap have outer diameters substantiallyless than the outer diameters of the adjacent insulative cylinders.

8. An electric discharge device according to claim 4, wherein theinsulative cylinder and insulative cap between which said controlelectrode is interposed include annular opposed recesses in which saidthird of said annular metal members is received thereby to imbed same inthe Wall structure of said device afforded by said insulative cylinderand cap.

9. A voltage tunable magnetron adapted for operating with a staticmagnetic field extending axially therethrough comprising an anodecircuit including 'a plurality of segments supported in cylindricalarray in mutually spaced relation, a non-emissive electrode supported insaid envelope concentrically within the opening defined by said segmentsand cooperating with said segments to define an annular interactionspace, a unipotential filamentary electron emissive electrode axiallyclosely spaced relative to said interaction space, an annular controlelectrode surrounding said filamentary electrode and axially closelyspaced relative to said interaction space, the

opposed ends of said non-emissive and emissive electrodes, the adjacentends of said anode segments and said control electrode defining anelectric field at the end of said interaction space effective forcontrollably directing electrons axially from said emissive electrodeinto said interaction space, and said electron emissive electrodecomprising only a single filamentary element including a pair ofcontra-wound helical portions, whereby said emissive electrode iseffective for supplying electrons for direction into said interactionspace with minimal introduction of undesired magnetic field componentsinto the regions of said electric field and interaction space.

10. A voltage tunable magnetron according to claim 9 wherein saidnon-emissive and emissive electrodes are electrically spaced to enableoperation thereof at differend of said'envelope and disposedconcentrically within the opening defined by said segments andcooperating therewith to define an annular interaction space, aunipotential filamentary electron emissive electrode axially closelyspaced relative to said interaction space, an annular control electrodesurrounding said filamentary electrode and axially closely spacedrelative to said interaction space, the opposed ends, of saidnon-emissive and emissive electrodes, the adjacent ends of said anodesegments and said control electrode defining an electric field at theend of said interaction space effective for controllably directingelectrons axially from said emis-' sive electrode into said interactionspace, said electron emissive electrode comprising only a singlefilamentary element including a pair of contra-wound helical'portions,whereby said emissive electrode is efiective for supplying electrons fordirection into said interaction space with minimal introduction ofmagnetic field components into the regions of said electric field andinteraction space, and said filamentary element including'integral legportions at the ends of said helical portions, extending parallel to theaxis of said helical portions at diametrically opposed points spaced asubstantial distance outwardly of said helical portions, and said legportions extending through and being sealed directly in apertures in aceramic cap closing the other end of said envelope, whereby saidemissive electrode is stably mounted for minimizing movement of saidemissive electrode relative to the other electrodes defining saidelectric field.

References Cited in the file of this patent UNITED STATES PATENTS WrightJuly 20, 1943 Glauber Mar. 1, 1949 Wing Sept. 12, 1950 Kumpfer Mar. 31,1953 Peters et a1. Oct. 15, 1957

